|Scientific Name||Helianthus annuus L.|
|Common Names||English: Sunflower; German: Sonnenblume; French: Tournesol; Spanish: Girasol|
|Description||Tall, coarsly-leafed plant with a distinctive large, yellow bloom, growing to a height of 60 - 390 cm (1.97 - 12.79 ft) and forming a taproot. H. annuus is native to North America.|
Large heart-shaped leaves.
Cotyledons oblong, 15-40 mm (0.59 - 1.57 inch) long, joined at the bases, smooth. First few true leaves opposite, dull green, covered with short bristly hairs that are rough to touch. Margins weakly round-toothed. Subsequent leaves alternate.
Oblong, 15-40 mm (0.59 - 1.57 inch) long, joined at the bases, smooth.
Large, stout central stem.
7.5 - 30 cm (2.95 - 11.81 inch) long; the lowest ovate, usually heart-shaped, edged with irregular teeth; the upper, smaller and more narrow.
Large heads, 7.5 - 15 cm (2.95 - 5.9 inch) wide. More than 10 flowers per plant. Ovate bracts enclose heads edged with bristles and narrow abruptly into a slender tip. Flower made up of 1,000 to 2,000 individual flowers joined at a common receptacle. The flowers around the circumference are ligulate ray flowers without stamens or pistils. The remaining flowers are perfect flowers (with stamens and pistils).
Achenes 3-15 mm (0.118 - 0.59 inch) long. Pappus scales 2-3.5 mm (0.078 - 0.137 inch) long. Dry casing enclosing a white seed; flattish but plump; drop off easily.
Seedlings can emerge from depths of more than 10 cm (3.93 inch). Germination in spring.
Viability of Seeds
Woodland meadows, cultivated and abandoned fields, pastures, areas along railroads and roads, and urban waste areas, dry open plains and foothills.
Fertile loamy soil, often thrives in soil with a high clay or gravel content.
H. annuus reduces significantly crop yield because of its aggressive growth habit, canopy structure and competitiveness. The leaves are inedible for humans and livestock because of high nitrogen content.
Useful non-chemical contribution to Integrated Weed Management
Cultivation to a depth of 20 cm (7.87 inch) reduces survival of sunflower.
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